Distorted–octahedral site‒occupation induced high efficiency broadband near infrared emission in LiScGe2O6:Cr3+ phosphor

The discovery of high efficiency broadband Near-infrared (NIR) emission phosphor for phosphor-converted light-emitting diodes (NIR-pc-LEDs) is of importance for optoelectronic device and the emerging applications. Herein, a highly efficient broadband...

The Site Occupancy Assessment in Beryl Based on Bond-Length Constraints

The site preference for each cation and site in beryl based on bond-length calculations was determined and compared with analytical data. Tetrahedral SiO4 six-membered rings normally have no substitutions which results from very compact Si4+–O bonds in tetrahedra. Any substitution except Be would require significant tetrahedral ring distortion. The Be tetrahedron should also be negligibly substituted based on the bond-valence calculation; the tetrahedral Li–O bond length is almost 20% larger than Be2+–O. Similar or smaller bond lengths were calculated for Cr3+, V3+, Fe3+, Fe2+, Mn3+, Mg2+, and Al3+, which can substitute for Be but also can occupy a neighboring tetrahedrally coordinated site which is completely vacant in the full Be occupancy. The octahedral site is also very compressed due to dominant Al with short bond lengths; any substitution results in octahedron expansion. There are two channel sites in beryl: the smaller 2b site can be occupied by Na+, Ca2+, Li+, and REE3+ (Rare Earth Elements); Fe2+ and Fe3+ are too small; K+, Cs+, Rb+, and Ba2+ are too large. The channel 2a-site average bond length is 3.38 Å which allows the presence of simple molecules such as H2O, CO2, or NH4 and the large-sized cations-preferring Cs+.

NANOPARTICLE FABRICATION OF COxNi1-xFe2O4 (x=0,0.25,0.5,0.75,1.0) USING CO-PRECIPITATION METHODE AT LOW TEMPERATURE

<p>Nanoparticle Co_xNi_1-xFe₂O₄ has been successfully synthesized using co-precipitation method at low temperature 120^oC by variation of concentration value (x=0; 0.25; 0.5; 0.75; 1.0). Crystal structure and size of crystallite increase with increasing cobalt concentration. There is a difference of lattice between theoretical and experimental. Increase the cobalt concentration in Co_xNi_1-xFe₂O₄ nanoparticle affected to the bond length between cation-anion on tetrahedral site and octahedral site. Because of the distortion, the crystallite where imperfectly formed and crystal defect occurred. It is indicated by the microstrain value that describes the magnitude of the strain in crystal.</p>